I was surprised at the size of the capacitors
   so that added a bit of square inches to the
   PC board. Back in the old days (60's) we used
   large metal can capacitors that were oil filled
   for our CD systems and vac tubes of course.

   Those caps store the spark energy instead of
   being stored in the coils. CD coils
   run cool as they are simply used as pulse
   transformers.

   Boards cost about 65 cents per square inch
   Plus a fixed cost of $55 for tooling.

   The caps are the 4 big boxes in the center of the PC
   Board. I'll use my favorite heat sink and
   TV connector for the output to the coil.
   This is for one spark plug on one rotor.
   The trailing plug does not need it and
   and any back up ignition can be used on the
   trailing rotor.

   This requires 4 Hall Effect devices
   per plug to trigger every 10 degrees for
   40 degrees after 22 degrees BTDC.
   In other words 20 BTDC, 10 BTDC, TDC and
   10 degrees after TDC with no RPM limit
   such as MSD's have problems with.
   One cap for each spark.

   The whole idea here is to see if it will
   cut the fuel burn.

   I'll see if I can get Mazdatrix to test it on
   the dyno. I'll loan it to them for use on
   what ever engine they are fooling with at
   the moment.

   It uses one 400 watt 220 Volt AC off the shelf 12 V power
   supply for up to 6 PC boards if you want to implement
   that many on a 3 rotor.

   Paul Lamar

It would appear that isolation devices are needed between the four 2mfd caps
and the coil.  When trigger is low, there is a low impedance to ground thru
the lower FET of the half-bridge, essentially putting the caps of the
untriggered drivers in parallel with the coil.

   Victor Roberts,

Yes I see what you are saying. It is helpful I have other engineers looking
over my shoulder.

I need some more switches in there.
Thanks Victor. Do you have any suggested circuits?

Paul Lamar

The current configuration still leaves the 3 untriggered caps with one lead
open. This does not put them in parallel with the coil or am I missing
something?
Dick Handverger


Thanks Dick.
First condition.  All caps are fully charged through the coil.
This group is in series with the coil. The problem Victor pointed out was
when any lower gate closed all caps now in parallel would be discharged
through that gate bypassing the coil as that would be the path of
least resistance. The coil would see no current flow.

I think I need Triac's in series with all caps to prevent that from
happening so only the coil sees the sudden increase in current.

Triacs are bidirectional switches unlike most semiconductors.
They look like a relay contacts. Relays contacts don't care
which way the current flows.

All Triacs need to be on when no trigger pulse is occurring so
the caps can charge through the coils. Only the Triac that
is associated with the trigger pulse stays on when the trigger
occurs.

I have yet to figure out the logic on how to do that
short of a computer. Any suggestions?

Here is an incremented schematic.

---------------------------------------------

Here is the truth table. Output refers to the triac.
0 is off and a 1 is on.

Looks like I will need a programmable logic chip
with 4 inputs and 4 outputs unless somebody can
come up with a better idea.

The all triggers on condition never happens.
In that case there is an error so all triacs
should be off.

Paul Lamar